1. Field of the Invention
This invention relates to a stimulable phosphor sheet conveyance apparatus for a system in which stimulable phosphor sheets are exposed to a radiation passing through an object to have a radiation image stored thereon, the stimulable phosphor sheets are exposed to stimulating rays which cause them to emit light in proportion to the stored radiation energy, the emitted light is detected and converted into electric image signals which are used to reproduce a visible image from the read-out image information, the stimulable phosphor sheets are exposed to erasing light for releasing radiation energy remaining thereon after read-out, and the erased stimulable phosphor sheets are reused for recording radiation images. This invention particularly relates to a stimulable phosphor sheet conveyance apparatus for conveying stimulable phosphor sheets into and out of an erasing section of such a system.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed for example in Japanese Unexamined Patent Publication No. 56(1981)-11395 and U.S. Pat. Nos. 4,258,264, 4,315,318, 4,387,428 and 4,276,473, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as a part of the human body to have a radiation image stored thereon, and is scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed so as to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used only for temporarily storing the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheets be used repeatedly.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining on the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored thereon should be erased as described, for example, in Japanese Unexamined Patent Publication No. 56(1981)-12599 and U.S. Pat. No. 4,470,619. The stimulable phosphor sheet can then be used again for radiation image recording.
For enabling the aforesaid radiation image recording and read-out method to be carried out at high efficiency using compact equipment, it is advisable for the read-out of the image information from the stimulable phosphor sheets carrying the radiation image of the object stored thereon and the erasure of the radiation energy remaining on the stimulable phosphor sheets after read-out to be carried out consecutively in a continuous operation in one and the same apparatus. When stimulable phosphor sheets recorded with radiation images are loaded into such an apparatus integrally combining a read-out section and an erasing section, they are first subjected to read-out of the stored image information in the read-out section and then immediately subjected to erasure of the remaining radiation energy in the erasing section, whereafter they are discharged from the apparatus in a state reusable for the recording of radiation images thereon. Further, if a radiation image recording section is also built into the aforesaid integrated apparatus, it becomes possible to carry out image recording, image read-out and the erasure of the remaining radiation energy consecutively in a single apparatus.
The apparatus integrating the read-out and erasing sections or integrating these sections together with the recording section should be fabricated as compactly as possible. It is therefore preferable to position the read-out and erasing sections one above the other and to convey the read-out sheets from the read-out section to the erasing section by a conveyance means employing belts or the like. In this case, however, if the stimulable phosphor sheets are simply conveyed from the read-out section to the erasing section by an ordinary belt, the surface of the sheets for the recording of radiation images (hereinafter referred to as the stimulable phosphor side) will face in opposite directions in the read-out and erasing sections. More specifically, if the stimulable phosphor side of a sheet faces upward in the read-out section, it will face downward when the sheet arrives at the erasing section. As a result, in order to expose the stimulable phosphor sheets to erasing light, it becomes necessary to make the conveyor belt and other components of the conveyance means in the erasing section from transparent materials and to provide the erasing light sources below the conveyance means. This is undesirable from the point of erasing efficiency and the like.
To overcome this problem without having to turn the stimulable phosphor sheet over after it arrives at the erasing section, it is general practice to provide a switchback mechanism for once reversing the direction of travel of the sheet as it is conveyed between the read-out section and the erasing section and a guide plate whose operation is interlinked with that of the switchback mechanism so as to change the course along which the sheet is conveyed. However, this solution is disadvantageous in that the need to provide the guide plate interlinked with the switchback mechanism complicates the structure of the apparatus and results in higher fabrication cost, and also in that the guide plate is apt to scratch the stimulable phosphor side of the sheets, which is a particularly fatal defect in a system that repeatedly reuses the stimulable phosphor sheets and that carries out read-out of the image information from the stimulable phosphor sheets by scanning their stimulable phosphor sides with stimulating rays.